This invention relates to a device for detecting defective containers, and to a test head and seal suitable for use in such a device.
Containers such as plastic barrier containers are in widespread use in many industries, including the pharmaceutical and the food industries. It is essential that such containers be leak proof if they are to perform their intended function. For example, plastic barrier containers can be designed to accept a metal closure which is secured to the container by metal seaming in a conventional manner. The defect rate of such plastic containers is extremely low, often less than 0.001 percent. Defects that do exist normally come in the form of a pin hole in the body of the container or a grossly deformed flange. Even this low defect rate can present a substantial problem, because even one defect entering a rotary retort can cause substantial loss of product and down time.
Leak detectors of various sorts are known in the art. For example, Nowicki U.S. Pat. No. 3,762,213 discloses a system for detecting leaks in bottles. A cam-operated test head is lowered by a first cam into sealing engagement with the bottle, and then a diaphragm is raised with a spring operating against a second cam. The cams are reciprocated relative to the bottle by a hydraulic cylinder to complete a test cycle. The Nowicki leak detector relies on oscillating cams positioned above a conveyor to operate a test head that is substantially fixed in position with respect to the direction of motion of the conveyor.
Weber U.S. Pat. No. 3,413,841 discloses a leak tester utilizing a rotary platform onto which containers are fed by a first starwheel, and from which containers are removed by a second starwheel. As shown in FIGS. 2a and 2b, a first cam is provided below the support surface for the containers, and this first cam raises and lowers the containers in various portions of the cycle. A second cam is positioned above the support surface for the containers, and the second cam is used to draw a vacuum.
The present invention is directed to an improved leak detector that is well suited for automatic use, and that provides improved sealing against the container and an efficient arrangement of parts.